1. Field of the Invention
The present invention relates to a stabilizing equipment having damping resistors for improving the stability of power transmission systems.
2. Prior Art
In recent years there has been a tendency toward the development of power transmission systems using longdistance and large capacity transmission lines. This has occurred because stations are apt to be located far from the consumer loads and to have increased power generating capacities. As a result, improved stability of power transmission systems has been an important requirement. While there are various ways of improving the power transmission system, considerable attention has been paid to the so-called damping resistor system from the viewpoint of effectiveness and economy of the power transmission system. In this damping resistor system, a damping resistor for suppressing the acceleration of a generator in the power source system is inserted between the terminals of the power source system at the time that a fault such as ground fault occurs in the power transmission system, so that the transient stability of the system is increased.
In such a stabilizing equipment of the prior art, however, the damping resistor inserted between the terminals of the power source is connected in parallel with a transmission line, and therefore it is necessary that the damping resistor be connected to the power source system after a faulted line is interrupted by circuit breakers. Otherwise, the above-mentioned effect whereby the system stability is increased cannot be attained. In the case where a main protective relay operates normally in a high speed protective equipment, the damping resistor is connected to the power source system when a faulted line is interrupted soon after the fault occurs. This means that the damping resistor is connected to the power source system shortly after the fault occurs, and accordingly the damping resistor improves the stability of the power transmission system. On the other hand, if the main protective relay fails to operate, a back up protective relay operates to interrupt the faulted line with a long time delay after the fault occurs and the damping resistor is connected to the power source system when the faulted line is interrupted. This means that the damping resistor is not connected to the power source system until the circuit breaks are opened long after the fault occurs and therefore the connection of the damping resistor does not show the above-mentioned improvement of the stability when the back up protective relay operates.